Rotor hub fairing system for a counter-rotating, coaxial rotor system

Abstract

A rotor hub fairing system includes an upper hub fairing, a lower hub fairing and a shaft fairing therebetween. The rotor hub fairing system is sized and configured to reduce the overall drag on a dual, counter-rotating, coaxial rotor system. Preferably, the rotor hub fairing is fully integrated. The shaft fairing preferably includes a minimal thickness at the midsection to reduce drag with an increasing thickness adjacent the upper and lower hub fairings to reduce the flow separation on the hub fairing surfaces without overly excessive drag. Other aerodynamic structures, such as a horizontal splitter and/or a plurality of turning vanes may be mounted to the shaft fairing to facilitate flow around the upper and lower hub fairings to reduce flow separation and drag.

1. A rotor hub fairing system for a coaxial rotor system comprising:
 an upper hub fairing defined about an axis; 
 a lower hub fairing defined about said axis; and 
 a shaft fairing between said upper hub fairing and said lower hub fairing, said shaft fairing defining an airfoil having a contoured midsection to reduce drag on the coaxial rotor system, said upper hub fairing and said lower hub fairing being rotatable with respect to said shaft fairing. 
 
   
   
     2. The rotor hub fairing system as recited in  claim 1 , wherein said shaft fairing is bearing mounted relative said upper hub fairing and said lower hub fairing for independent rotation relative thereto. 
   
   
     3. The rotor hub fairing system as recited in  claim 2 , wherein said pitching axis is generally parallel to an axis of rotation of the coaxial rotor system. 
   
   
     4. The rotor hub fairing system as recited in  claim 2 , wherein said pitching axis is defined at a quarter chord of said airfoil. 
   
   
     5. The rotor hub fairing system as recited in  claim 1 , wherein said shaft fairing includes an airfoil which defines a pitching axis which extends through said upper hub fairing and said lower hub fairing. 
   
   
     6. The rotor hub fairing system as recited in  claim 1 , wherein said shaft fairing is generally of an hour glass shape in a cross-section transverse to said shaft fairing taken along said axis. 
   
   
     7. The rotor hub fairing system as recited in  claim 1 , wherein said shaft fairing includes a thickness distribution in which a minimal thickness occurs within said contoured midsection. 
   
   
     8. The rotor hub fairing system as recited in  claim 1 , wherein said shaft fairing includes a NACA 0028 airfoil along said contoured midsection and an NACA0042 airfoil adjacent said upper hub fairing and said lower hub fairing. 
   
   
     9. The rotor hub fairing system as recited in  claim 1 , wherein a trailing edge of said shaft fairing extends beyond a periphery of said upper hub fairing and said lower hub fairing. 
   
   
     10. The rotor hub fairing system as recited in  claim 1 , further comprising a splitter airfoil transverse to said shaft fairing. 
   
   
     11. The rotor hub fairing system as recited in  claim 10 , wherein said splitter airfoil extends from said contoured midsection of said shaft fairing, said shaft fairing includes a thickness distribution in which a minimal thickness occurs within said contoured midsection. 
   
   
     12. The rotor hub fairing system as recited in  claim 10 , wherein a trailing edge of said splitter airfoil extends beyond a trailing edge of said shaft fairing. 
   
   
     13. The rotor hub fairing system as recited in  claim 10 , wherein said splitter airfoil defines a maximum thickness adjacent a mid-chord position. 
   
   
     14. The rotor hub fairing system as recited in  claim 10 , wherein said splitter airfoil includes a span which is less than a diameter of said upper hub fairing. 
   
   
     15. The rotor hub fairing system as recited in  claim 1 , further comprising a plurality of turning vanes. 
   
   
     16. The rotor hub fairing system as recited in  claim 15 , wherein said plurality of vanes includes an upper turning vane and a lower turning vane. 
   
   
     17. The rotor hub fairing system as recited in  claim 15 , wherein said upper turning vane and said lower turning vane are cambered toward said respective upper and lower hub fairing. 
   
   
     18. The rotor hub fairing system as recited in  claim 1 , wherein said upper hub fairing, said lower hub fairing, and said shaft fairing are integrated to operate as a single aerodynamic element. 
   
   
     19. The rotor hub fairing system as recited in  claim 1 , wherein said shaft fairing is contoured to have a minimal thickness at a center region of said contoured midsection. 
   
   
     20. The rotor hub fairing system as recited in  claim 1 , wherein said airfoil is defined along said axis, said axis generally transverse to a freestream direction during forward flight. 
   
   
     21. The rotor hub fairing system as recited in  claim 1 , wherein said upper hub fairing and said lower hub fairing define a diameter about said axis, said shaft fairing defining said airfoil along said axis, said axis generally transverse to a freestream direction during forward flight. 
   
   
     22. A rotor hub fairing system for a coaxial rotor system comprising:
 an upper hub fairing defining an upper hub fairing diameter; 
 a lower hub fairing defining a lower hub fairing diameter; and 
 a shaft fairing between said upper hub fairing and said lower hub fairing, said shaft fairing defining a shaft fairing chord to at least one of said upper and lower hub fairing diameters (c/D) of between 0.90 D to 1.25 D, said upper hub fairing and said lower hub fairing being rotatable with respect of said shaft fairing. 
 
   
   
     23. The rotor hub fairing system as recited in  claim 22 , wherein said shaft fairing defines a shaft fairing chord that is between 110% to 120% chord relative to at least one of said upper and lower hub fairing diameter. 
   
   
     24. The rotor hub fairing system as recited in  claim 22 , wherein said upper hub fairing diameter is generally equal to said lower hub fairing diameter. 
   
   
     25. The rotor hub fairing system as recited in  claim 22 , wherein said shaft fairing includes a thickness distribution in which the minimal thickness occurs within a contoured midsection. 
   
   
     26. The rotor hub fairing system as recited in  claim 22 , wherein a trailing edge of said shaft fairing extends beyond said upper hub fairing diameter. 
   
   
     27. The rotor hub fairing system as recited in  claim 22 , wherein said airfoil is defined along said axis, said axis generally transverse to a freestream direction during forward flight. 
   
   
     28. A coaxial rotor system comprising:
 an upper rotor system including an upper rotor hub which rotates about an axis of rotation; 
 an upper hub fairing which at least partially surrounds a portion of said upper rotor hub; 
 a lower rotor system including a lower rotor hub which rotates about said axis of rotation; 
 a lower hub fairing which at least partially surrounds a portion of said lower rotor hub; and 
 a shaft fairing between said upper hub fairing and said lower hub fairing, said shaft fairing having a pitching axis generally parallel to said axis of rotation, said upper hub fairing and said lower hub fairing being rotatable with respect to said shaft fairing. 
 
   
   
     29. A rotor hub fairing system for a coaxial rotor system comprising:
 an upper hub fairing defined about an axis; 
 a lower hub fairing defined about said axis; 
 a shaft faring between said upper hub fairing and said lower hub fairing, said shaft fairing including a thickness distribution in which a minimal thickness occurs within a contoured midsection; and 
 a splitter airfoil mounted transverse to said shaft fairing.